1. Field of the Invention
The present invention relates to indwelling medical devices, such as catheters, the material of which is impregnated with one or more antimicrobial agents to inhibit the growth of bacterial and fungal organisms, such as staphylococci, other gram-positive bacteria, gram-negative bacilli and Candida. The invention also relates to a method of impregnating the indwelling medical device with one or more antimicrobial agents, such as minocycline and rifampin.
2. Description of the Prior Art
Indwelling medical devices including vascular catheters are becoming essential in the management of hospitalized patients by providing venous access. The benefit derived from these catheters as well as other types of medical devices such as peritoneal catheters, cardiovascular devices, orthopedic implants and other prosthetic devices is often offset by infectious complications. The most common organisms causing these infectious complications are Staphylococcus epidermidis and Staphylococcus aureus. In the case of vascular catheters, these two organisms account for almost 70-80% of all infectious organisms, with Staphylococcus epidermidis being the most common organism. Candida albicans, a fungal agent, accounts for about 10-15% of catheter infections.
Another common hospital-acquired infection is urinary tract infection (UTI). The majority of cases of UTI are associated with the use of urinary catheters, including transurethral foley, suprapubic and nephrostomy catheters. These urinary catheters are inserted in a variety of populations, including the elderly, stroke victims, spinal cord-injured patients, post-operative patients and those with obstructive uropathy. Despite adherence to sterile guidelines for the insertion and maintenance of urinary catheters, catheter-associated UTI continues to pose a major problem. For instance, it is estimated that almost one-quarter of hospitalized spinal cord-injured patients develop symptomatic UTI during their hospital course. Gram-negative bacilli account for almost 60-70%, enterococci for about 25% and Candida species for about 10% of cases of UTI.
Colonization of bacteria on the surfaces of the catheter or other part of the device can produce serious patient problems, including the need to remove and/or replace the implanted device and to vigorously treat secondary infective conditions. A considerable amount of attention and study has been directed toward preventing such colonization by the use of antimicrobial agents, such as antibiotics, bound to the surface of the materials employed in such devices. In such attempts the objective has been to produce a sufficient bacteriostatic or bactericidal action to prevent colonization.
Various methods have previously been employed to coat the surfaces of medical devices with an antibiotic. For example, one of the simplest methods would be to flush the surfaces of the device with a solution of the antibiotic combination. Generally, coating the surfaces by a simple flushing technique would require convenient access to the implantable device. For example, catheters are generally amenable to flushing with a solution of rifampin and minocycline or rifampin and novobiocin. For use in flushing solutions, the effective concentration of the antibiotic would range from about 1 to 10 .mu.g/ml for minocycline, preferably about 2 .mu.g/ml; 1 to 10 .mu.g/ml for rifampin, preferably about 2 .mu.g/ml; and 1 to 10 .mu.g/ml for novobiocin, preferably about 2 .mu.g/ml. The flushing solution would normally be composed of sterile water or sterile normal saline solutions.
Another known method of coating the devices would be to first apply or absorb to the surface of the medical device a layer of tridodecylmethyl ammonium chloride (TDMAC) surfactant followed by an antibiotic coating layer. For example, a medical device having a polymeric surface, such as polyethylene, silastic elastomers, polytetrafluoroethylene or Dacron, can be soaked in a 5% by weight solution of TDMAC for 30 minutes at room temperature, air dried, and rinsed in water to remove excess TDMAC. Alternatively, TDMAC precoated catheters are commercially available. For example, central vascular catheters coated with TDMAC are available from Cook Critical Care, Bloomington, Ind. The device carrying the absorbed TDMAC surfactant coating can then be incubated in an antibiotic solution for up to one hour or so, allowed to dry, then washed in sterile water to remove unbound antibiotic and stored in a sterile package until ready for implantation. In general, the antibiotic solution is composed of a concentration of 0.01 mg/ml to 60 mg/ml of each antibiotic in an aqueous pH 7.4-7.6 buffered solution, sterile water, or methanol. According to one method, an antibiotic solution of 60 mg of minocycline and 30 mg of rifampin per ml of solution is applied to the TDMAC coated catheter.
A further method known to coat the surface of medical devices with antibiotics involves first coating the selected surfaces with benzalkonium chloride followed by ionic bonding of the antibiotic composition. See, e.g., Solomon, D. D. and Sherertz, R. J., J. Controlled Release, 6:343-352 (1987) and U.S. Pat. No. 4,442,133.
Other methods of coating surfaces of medical devices with antibiotics are taught in U.S. Pat. No. 4,895,566 (a medical device substrate carrying a negatively charged group having a pKa of less than 6 and a cationic antibiotic bound to the negatively charged group); U.S. Pat. No. 4,917,686 (antibiotics are dissolved in a swelling agent which is absorbed into the matrix of the surface material of the medical device); U.S. Pat. No. 4,107,121 (constructing the medical device with ionogenic hydrogels, which thereafter absorb or ionically bind antibiotics); U.S. Pat. No. 5,013,306 (laminating an antibiotic to a polymeric surface layer of a medical device); and U.S. Pat. No. 4,952,419 (applying a film of silicone oil to the surface of an implant and then contacting the silicone film bearing surface with antibiotic powders).
These and many other methods of coating medical devices with antibiotics appear in numerous patents and medical journal articles. Practice of the prior art coating methods results in a catheter or medical device wherein only the surface of the device is coated with the antibiotic. While the surface coated catheter does provide effective protection against bacteria initially, the effectiveness of the coating diminishes over time. During use of the medical device or catheter, the antibiotics leach from the surface of the device into the surrounding environment. Over a period of time, the amount of antibiotics present on the surface decreases to a point where the protection against bacteria is no longer effective.
Accordingly, there is a need for a catheter or medical device that can remain in vivo for extended periods of time without losing its antimicrobial efficacy. There is also a need for an easy and inexpensive method of applying an antimicrobial agent to a medical device, such as a catheter, that provides protection against bacterial and fungal organisms for extended periods of time.